Manufacture of ammonium bifluoride



Jan. 20, 1942. A. R. BOZARTH MANUFACTURE OF AMMONIUM BIFLUORIDE FiledApril 28, 1939 INVENTOR.

ATTORNEY.

Patented Jan. 20, 1942 2,270,493 MANUFACTURE or AMMONIUM BIFLUORIDE AbeR. Bozarth, Clevelandohio, ,assignor to The Harshaw Chemical Company,Elyria, Ohio, a

corporation of'Ohio Application April 28, 1939, Serial No.-270,601

4 Claims. i 01. 23-88) This invention relates to manufacture of ammoniumbifiuoride. I r

An object of the invention is to provide a process for production ofthis compound by direct union of NH3 and HF, both in a substantiallyanhydrous state, and for the removal of the product from the reactionapparatus in the form of a finely divided solid.

A further object is to provide simple and cheap but effective apparatusfor use in performing the novel process.

In my copending application, Serial No. 204,541, filed April'27, 1938,now Patent No. 2,156,273, issued May 2, 1939, I have described a similarmethod of producing NHiFHF. 'In that patent, however, the product wasrecovered as a liquid and allowed to solidify as a mass or convertedinto flakes on a cooling drum. In accordance with the present invention,the product may be recovered in the form of a solid which is more finelydivided and preferably takes a form which may be termed a snow, being afine precipitate from a gas phase reaction. By proper control of theflow of reactants and cooling air a less fine1y divided material(solidified droplets) may be obtained with the form of apparatus shownin Fig. 1. It is, however, preferred to operate in a manner to produce asnow.

In the drawing, Fig. l is a schematic, vertical sectional view of anapparatus adapted to be used in practicing the invention; Fig. 2 is asimilar view of a modified form of apparatus; Fig. 3 is a similar viewof a further modified apparatus and Fig. 4 is a section on the line 4-4of Fig. 1.

In Fig. l I have shown supply lines l and II for Nlh and HF gases, itbeing understood that for regulation of temperature and the physicalstate of the product, the line In may supply a mixture of N133 and airor other inert gas while the line H may supply a mixture of HF and airor other inert gas. The flow of gases from the lines l0 and II iscontrolled by suitable valves l2 and I3 respectively. The so regulatedgases are brought together in pipe section l4 and there react to formNl-liFl-lF, which, in gaseous state, impinges upon a rapidly revolvingdisk l5 and is distributed over the upper face thereof to an air streamcreated by fan elements I6 and is thereby cooled to a snow which settlesdown and is removed in that condition.

As will be clear from the drawing, the pipe section I4 extends into aclosed chamber I'I, having a hopper bottom I8 provided with a rotarydischarge device I9 by means of which solid mamitting substantialpassage of gas. Suitable air inlet openings 20 are provided near the topof the hopper portion l8. Attached to the vertical wall of the enclosureH in any suitable manner is an air-supply conduit in the form of aspider, each leg 2l of which has the cross-section indicated in Fig. 4and registers with one of the openings 20. Centrally, the spider isprovided with an upstanding cylindrical portion 22 terminating in anoutwardly and upwardly directed flange 23. Suitably mounted on thespider is a motor support 24 upon which is mounted an electric motor 25.The armature of the motor 25 carries the disk l5 and the fan elementsI6. At the top of the enclosure I1 is provided an air outlet 26 belowwhich are bafiles 21.

In operation, NH3 and HF in anhydrous state (combined moisture contentless than 5%) are brought together in the pipe section I4, the initialtemperatures or compositions being so adjusted that NI-IrFI-IF impingesupon the disk I5 while still in gaseous condition.- I 'his gas entersthe air stream formed by the fan elements I6 and shortly solidifies intoa snow, which settles to the bottom and is removed through the dischargel9. By suitable control of the temperatures, it is possible to cause theNHiFHF to assume the form of small droplets before it is solidified,thereby varying the physical character of the resulting solid.

In Fig. 2 I have shown a modified form of apparatus wherein compressedair is used for chilling the gaseous NH4FHF. In this view, the enclosureis indicated by the numeral 28 and the hopper bottom by the numeral 29.The bottom is provided with a rotary discharge 30 and air outlets 3|covered by baffles 32. Sealed through the top wall of the enclosure 28is a cylindrical element 33 which surrounds the lower end of thereaction tube 34. The tube 34 is supplied with reactants through pipes35 controlled by suitable valves 36. Compressed air is supplied from theline 31 to the interior of the element 33. A composite stream of air andNHiFHF impinges upon a suitably supported, conical, spreading element 38and is converted into solid material which collects in the hopper 29 andis removed through the discharge 30.

As in the form shown in Fig. 1. suitable temperature control ismaintained by control of the rate of fiow of gases, proportion ofdiluent. gas, if any, initial temperature of reactants and insulationwhere necessary. These factors preferably are controlled so that nosolid material terial may be continuously removed without per- 5.3 cancollect on the spreading cone and preferably so that no liquid comesinto contact therewith. The enclosure may be made relatively much largerthan shown in the drawing for the purpose of reducing turbulence ofgases therein.

In Fig. 3 I have shown an apparatus of very simple construction which isadapted especially for relatively low gas velocities. In this form, theenclosure is indicated by the numeral 39 and is provided with a hopperbottom 40 and a rotary discharge 4|. The top wall 42 is provided with anair outlet 43 below which is a conical bafile 44. NH3 or a mixturethereof with air or other diluent gas is fed through supply line 45,while HF or a mixture thereof with air or other diluent is fed through asupply line 46. These gases are brought together and react in the pipesection 41 which delivers into the enclosure. Also delivering into theenclosure is an air duct 48, which is disposed at an angle to the pipesection 41 so that the gas streams mingle whereby the NH4FHF is chilledto a snow. The ends of the ducts 41 and 48 may be provided with specialmixing nozzles such as slit openings parallel to each other, for highergas velocities.

Broadly stated, the novel process comprises mixing gaseous ammoniumbifiuoride with a cooling gas whereby to convert the same into a solid,preferably a finely divided or a snow-like solid.

Ammonia and hydrofluoric acid, having not more than five percent ofmoisture are brought together in proportions of one mol NI-Ia to twomols HF, in a reaction chamber or space. The heat of reaction serves tomaintain the product gaseous at the point of reaction. The gaseousreaction product is then mixed with air or other inert gas at aconsiderably lower temperature. Assuming a pressure of substantially oneatmosphere, the temperature of the gas issuing from thereaction chambershould be above 240 C., the boiling point of ammonium bifiuoride. Itshould not be higher than 3 C. and preferably not above 250 C. Thecooling air, on the other hand, Should be below 50 C. A very suitabletemperature for the cooling air is 20 to 25 C. The resulting finelydivided solid is allowed to settle and is then removed for use or sale.

Having thus described my invention, what I claim is:

1. A process of making ammonium bifluoride comprising contacting gaseousNH: and gaseous HF in approximately the proportions in which theycombine to form NH4FHF, both gases being substantially anhydrous, andcontacting the resulting gaseous NH4FHF with air at a temperature belowC.

2. A process of making ammonium bifiuoride comprising contacting gaseousNl-I3 and gaseous HF in approximately the proportions in which theycombine to form NHiFHF, both gases being substantially anhydrous andcontacting the resulting material at a temperature not lower than 240 C.with air at a temperature below 50 C.

3. A process of making ammonium bifluoride comprising contacting gaseousNH: and gaseous HF in approximately the proportions in which theycombine to form NH4FHF, both gases being substantially anhydrous and atleast one thereof being diluted with air, and contacting the resultingmaterial at a temperature not lower than 240 C. with air at atemperature below 50 C. whereby to precipitate a finely divided solidammonium bifiuoride.

4. A process for the manufacture of ammonium bifluoride in finelydivided solid form which comprises producing a thin jet of air in anenclosure, maintaining said thin jet of air by supplying thereto air ata temperature below 50 C., and bringing into contact with said jet ofair a gaseous body produced by bringing together NH: and HF inapproximately the proportions in which they combine to form NHiFHF, boththe NHa and the HF being substantially anhydrous and said gaseous bodybeing at a temperature not lower than 240 C. before contact with saidjet of air.

ABE R. BOZARTH.

